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United States Patent |
5,306,410
|
Farmer
|
April 26, 1994
|
Method and device for electrically coupling a conductor to the metal
surface of an electrolytic cell wall
Abstract
An external electrical metal conductor strap mounted a spaced distance from
the external steel wall of an electrolytic cell where the steel wall is
internally joined to the cathodes of the cell with the interspace between
the external metal conductor strap and the external steel wall filled with
an electrical conductor filler metal so that the external metal conductor
strap and the external steel wall of the cell is in continuous electrical
contact across the entire surface area interface between the external
metal conductor strap and the external steel wall of the electrolytic
cell. The filler metal may be a metal alloy that melts and becomes liquid
at the normal operating temperature of the cell, or the filler metal may
be chosen so that it remains solid at the normal operating temperature of
the cell. Alternatively, the filler metal may be an alloy which does not
have a precise melting temperature, but rather a melting range through
which the alloy first softens, then forms a semi-liquid "slush," and
finally becomes a liquid as the temperature is increased.
Inventors:
|
Farmer; Thomas E. (1602 Biovu, Galveston, TX 77551)
|
Appl. No.:
|
985291 |
Filed:
|
December 4, 1992 |
Current U.S. Class: |
204/242; 204/279; 439/179 |
Intern'l Class: |
C25B 009/04 |
Field of Search: |
204/242,279
439/179
|
References Cited
U.S. Patent Documents
3591483 | Jul., 1971 | Loftfield et al. | 204/252.
|
3622944 | Nov., 1971 | Tsuchiya et al. | 439/179.
|
3873437 | Mar., 1975 | Pulver | 204/254.
|
3878082 | Apr., 1975 | Gokhale | 204/226.
|
3883415 | May., 1975 | Shibata et al. | 204/258.
|
3960697 | Jun., 1976 | Kircher et al. | 204/252.
|
4211269 | Jul., 1980 | McCutchen et al. | 204/252.
|
Foreign Patent Documents |
0466156 | Jan., 1992 | EP.
| |
0466266 | Jan., 1992 | EP.
| |
Other References
"Cerro Alloy Physical Data.multidot.Applications", brochure of Cerro Metal
Products, division of Cerro Corporation, Bellefonte, Pa.
|
Primary Examiner: Valentine; Donald R.
Attorney, Agent or Firm: Gordon; David P.
Claims
I claim:
1. A method for electrically coupling a conductor to a cathode metal
surface, comprising:
a) forming a cathode strap conductive plate in a manner such that when the
cathode strap conductive plate is attached to the cathode metal surface a
pocket interspace is formed between the cathode strap conductive plate and
the cathode metal surface;
b) attaching the cathode strap conductive plate to the cathode metal
surface to form the pocket interspace;
c) substantially filling the pocket interspace with a liquid or amorphous
conductive metal; and
d) attaching the conductor to the cathode strap conductive plate.
2. A method according to claim 1 further comprising:
sealing the pocket interspace between the cathode metal surface and the
cathode strap conductive plate.
3. A method according to claim 1 wherein:
the conductive metal is molten.
4. A method according to claim 1 further comprising:
forming a closable aperture in the cathode strap conductive plate.
5. A device for electrically coupling a conductor to a cathode metal
surface, comprising:
a) a cathode strap conductive metal plate;
b) first attachment means for attaching said cathode strap conductive metal
plate to the cathode metal surface, wherein said cathode strap conductive
metal plate is shaped to form a pocket interspace between said cathode
strap conductive metal plate and the cathode metal surface when said
cathode strap conductive metal plate is attached to the cathode metal
surface;
c) filler metal substantially filling said interspace; and
d) second attachment means for attaching said conductor to said cathode
strap conductive metal plate.
6. A device according to claim 5 wherein:
said filler metal is an alloy containing a metal chosen from the group
consisting of bismuth, lead, tin, cadmium, indium, silver, and copper.
7. A device according to claim 5, wherein:
said cathode strap conductive plate is provided with an opening, and said
device further comprises removable closure means for opening and closing
said opening.
8. A device according to claim 7, wherein:
said interspace is sealed by said first attachment means.
9. A device according to claim 5, wherein:
said filler material is molten when the cathode metal surface is at its
operating temperature.
10. A device according to claim 5, wherein:
said filler material is solid when the cathode metal surface is at its
operating temperature.
11. A device according to claim 5, wherein:
said filler material is amorphous when the cathode metal surface is at its
operating temperature.
12. A device according to claim 5, wherein:
said cathode metal surface is made from steel, and
said cathode strap conductive plate is made from copper.
13. An improved electrolytic cell, comprising:
a) a metal tank having a wall and a bottom for containing an electrolyte;
b) a first electrode suspended in said tank and electrically insulated from
said tank;
c) a second electrode extending from said wall of said tank and
electrically connected to said tank;
d) first attachment means for attaching a first conductor to said first
electrode;
e) a conductive strap plate;
f) second attachment means for attaching said conductive strap plate to
said wall, wherein said conductive strap plate is shaped such that when it
is attached to said wall, a pocket interspace is formed between said
conductive strap plate and said wall;
g) filler metal substantially filling said pocket interspace;
h) third attachment means for attaching a second conductor to said
conductive strap plate.
14. An improved electrolytic cell according to claim 13, wherein:
said conductive strap plate has an aperture extending therethrough.
15. An improved electrolytic cell according to claim 14, further
comprising:
removable closure means for opening and closing said aperture.
16. An improved electrolytic cell according to claim 13, wherein:
said filler metal is molten when said cell is operating.
17. An improved electrolytic cell according to claim 13, wherein:
said filler metal is solid when said cell is operating.
18. An improved electrolytic cell according to claim 13, wherein:
said fillter metal is amorphous when said cell is operating.
19. An improved electrolytic cell according to claim 13, wherein:
said wall is made from steel, and
said conductive strap plate is made from copper.
Description
FIELD OF THE INVENTION
The invention relates to a diaphragm or membrane or diaphragm-less
electrolytic cell for the production of chemicals such as chlorine by the
conversion of brine to caustic soda. More particularly, the invention
relates to the connection of an external conductor strap to the external
surface of the steel wall of the cell.
BACKGROUND OF THE INVENTION
Electrolytic cells for the production of chemicals such as chlorine and
caustic soda from aqueous solutions of NaCl generally include a carbon
steel cell within which anodes and cathodes are arranged and surrounded by
electrolyte. Normally several anodes or a networked grid-like anode is
placed within the cell from the bottom and the cathode walls of the cell
are connected by a similar grid-like network of fingers so that anodes and
cathodes are relatively evenly and closely spaced throughout the
electrolyte. Current is supplied to the cathodes via a conductor strap
(usually copper) attached to the exterior of the steel cell walls. Current
flows from the cathodes through the electrolyte to the anodes and is
carried from the anodes by a conductor which insulatingly passes through
the bottom of the cell.
Conventional methods of fastening the copper conductor strap to the
cathode's steel outer wall include fillet welding, brazing, or silver
soldering. Unfortunately, the copper-steel bond is difficult to create and
maintain and at best there remain air gaps between the copper strap and
the steel cell wall. At worst, fine cracks, fissures, or separations occur
in the steel wall of the cell or in the solder joint between the copper
and steel. A crack, fissure, or separation allows a small amount of
electrolyte to invade the crack, fissure, or separation. The invading
corrosive electrolyte may be brine or any other corrosive fluid which
spills onto or collects on the exterior surface of the cell. The corrosive
liquid begins to attack the cell wall at the small crack, fissure, or
separation. As the corrosive attack progresses, the crack, fissure, or
separation becomes larger and results in the invasion of progressively
more and more corrosive electrolyte. The end result is an ever compounding
corrosive attack.
Eventually, large quantities of iron oxide and other contaminants are
generated between the copper conductor strap and the cell's steel outer
wall. The buildup of rust and other contaminants causes the forcing of the
copper conductor strap away from the cell's outer wall. The force of
escaping electrolyte actually breaks the welded or brazed or soldered bond
between the outer wall and the copper conductor strap. At that point, a
very large crack or fissure or separation traps corrosive fluid between
the copper conductive strap and the cell's outer steel wall. If this
contagion of corrosive attack is unchecked, it will continue until the
copper strap is completely separated from the cell wall and the cell wall
begins to leak its electrolyte at a rate which renders the cell
functionally inoperative.
In practice, cells are removed from a productive cell line for repair prior
to such extensive damage. However, the cells are usually allowed to
function until the corrosive attack has pushed the copper conductor strap
away from the steel outer wall in several places. During the progression
of this corrosive attack, the electrolytic cell becomes progressively less
efficient as the cracks, fissures, or separations between the copper
conductor strap and the cathode's steel outer wall grows larger. The
resultant loss in efficiency is caused by several factors, primarily the
loss of continuous and uniform electrical conductivity between the copper
conductive strap and the cathode's outer cell wall. Under these
circumstances, parts of the damaged cathodes carry more electrical current
than others. This means that part of the cell is working less efficiently
than others. Electrical energy is lost, and the cell produces less product
per kilowatt hour as a result.
There have been improvements in the design of electrolytic cells, but most
of these improvements relate to the design and placement of the anode
rather than improvements to the cathode. For example, U.S. Pat. No.
3,591,483 to Loftfield et al (the complete disclosure of which is
incorporated herein by reference) discloses
Diaphragm-Type Electrolytic Cells; Use of Dimensionally Stable Anodes"
where the cell is provided with a metal base serving as a rigid support
and conductor for anodes and which supports the cell itself but is
insulated from the cell by a sheet of non-conductive material which also
provides an hydraulic seal to prevent leakage of electrolyte through the
bottom of the cell.
U.S. Pat. No. 3,873,437 to Pulver (the complete disclosure of which is
incorporated herein by reference) discloses an "Electrode Assembly for
Multipolar Electrolytic Cells" where an anode carried by a lateral surface
of a compartment wall is movable in a direction towards an opposed cathode
surface to maintain a narrow gap between the electrodes. A cathode carried
by the opposed lateral surface of the same compartment wall is optionally
provided with means for moving it in a direction towards the opposed anode
surface.
U.S. Pat. No. 3,878,082 to Gokhale (the complete disclosure of which is
incorporated herein by reference) discloses a "Diaphragm Cell Including
Means for Retaining a Preformed Sheet Diaphragm Against a Cathode" where a
preformed sheet material is used as a diaphragm through the use of
elasto-polymeric retainers.
U.S. Pat. No. 3,883,415 to Kokubu et al (the complete disclosure of which
is incorporated herein by reference) discloses a "Multiple Vertical
Diaphragm Type Electrolytic Cell for Producing Caustic Soda" where a large
number of unit cells are installed compactly in a cathode tank in
electrically parallel connection, each cell having two anode plates
interwelded by at least two conductive supporting rods which in turn are
connected to outer bus bars. An iron mesh cathode frame lined with an
asbestos diaphragm surrounds the anode plates. A corrosion resistant cap
is mounted on the iron mesh cathode and a bottom dish is inserted
thereinto. The upper part of the anode plates are secured by insulated set
screws.
U.S. Pat. No. 3,960,697 to Engler et al (the complete disclosure of which
is incorporated herein by reference) discloses a "Diaphragm Cell Having
Uniform and Minimum Spacing Between Anodes and Cathodes" where a
continuous net is provided between the anodes and the diaphragm to permit
minimum and uniform anode-cathode spacing while preventing the diaphragm
from adhering to the surface of the anodes.
U.S. Pat. No. 4,211,629 to Bess et al (the complete disclosure of which is
incorporated herein by reference) discloses an "Anode and Base Assembly
for Electrolytic Cells" where downwardly facing annular portions of the
anodes are welded to a perforated metal cell base cover which seals
electrolyte in the cell from the cell base eliminating corrosion in the
cell base and anode risers.
These improvements, while worthy in their own right, do not address the
problem discussed herein, namely, the connection of a conductor strap to
the exterior wall of the cell.
In connection with the present invention, it is also noted that bismuth
alloys are known to have very low-melting temperatures and low physical
strength and have been used as low temperature melting solders for safety
devices like sprinkler links, plugs in compressed gas tanks and in fire
alarm devices. Bismuth is a heavy, coarse crystalline metal which expands
when it solidifies. Water and antimony also expand on freezing, but
bismuth expands much more than the former, namely 3.3% of its volume. When
bismuth is alloyed with other metals, such as lead, tin, cadmium and
indium, this expansion is modified according to the relative percentages
of bismuth and other components present. As a general rule bismuth alloys
of approximately 50 per cent bismuth exhibit little change of volume
during solidification. Alloys containing more than this tend to expand
during solidification and those containing less tend to shrink during
solidification. After solidification, alloys containing both bismuth and
lead in optimum proportions grow in the solid state many hours afterwards.
Bismuth alloys that do not contain lead expand during solidification with
negligible shrinkage while cooling to room temperature.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a means for attaching
a conductor strap to the exterior steel cathode wall of an electrolytic
cell so that greater efficiency resulting in power savings is produced due
to increased electrical and thermal conductivity between the strap and the
cell wall.
It is also an object of the invention to provide a means for attaching a
conductor strap to the external wall of an electrolytic cell so that the
conductor strap and the steel wall will be in continuous electrical
contact across the entire surface area interface between the external
metal conductor strap and the external steel wall of the electrolytic
cell.
It is another object of the invention to provide protection from oxidation
and corrosion of both the conductor strap and the cell wall beneath the
conductor strap.
It is a further object of the invention to provide a method for coupling a
conductor to the cathode wall of an electrolytic cell which provides
functional advantages at reduced cost.
It is still another object of the invention to provide a low pressure seal
of small leaks which may arise in the cell wall under the conductor strap.
It is thus an object of the invention to provide for reduced and simplified
cell repairs and maintenance.
In accord with these objects which will be discussed in detail below, the
invention provides an external metal conductor strap mounted a spaced
distance from the external steel wall of an electrolytic cell where the
steel wall is internally joined to the cathodes of the cell and the
interspace between the external metal conductor strap and the external
steel wall is filled with an electrical conductor filler metal alloy. The
filler metal may be an alloy that melts and becomes liquid at the normal
operating temperature of the cell, or may be chosen so that it remains
solid at the normal operating temperature of the cell. Alternatively, the
filler metal may be an alloy which does not have a precise melting
temperature, but rather a melting range through which the alloy first
softens, then forms a semi-liquid "slush," and finally becomes a liquid as
the temperature is increased. In the case of an alloy which remains solid
during operation of the cell, it may be chosen from a group of alloys
which expand when solidified so that the filler metal alloy can be heated
and poured into the interspace between the conductor strap and the cell
wall wherein it is left to cool and expand forming a tight mechanical
bond.
Preferred aspects of the invention include: a copper conductor strap with
edges bent inward and welded, brazed or otherwise fastened to the steel
cell wall to create a pocket within which filler metal is placed. In one
embodiment, filler metal is introduced into the pocket in molten form
through a threaded filler plug. In another embodiment, a top portion of
the pocket formed by the copper strap is left open and filler metal is
dropped, placed or poured into the opening. In embodiments where filler
metal becomes molten, one or more drain plugs are provided to allow
removal of the filler metal from the interspace between the conductor
strap and the cell wall.
Additional objects and advantages of the invention will become apparent to
those skilled in the art upon reference to the detailed description taken
in conjunction with the provided figures.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of the entire electrolytic cell including
cover.
FIG. 2 is a perspective view, partially in cross section of a portion of an
electrolytic cell.
FIG. 3 is a cross sectional view along the line III--III of FIG. 1.
FIG. 4 is a view similar to FIG. 1, but showing another embodiment of the
invention.
FIG. 5 is a cross sectional view along the line V--V of FIG. 4.
DETAILED DESCRIPTION
Referring now to FIG. 1, an electrolytic cell 10 can be seen having walls
12 with an upper lip 26 and a lower lip 27. Lower lip 27 is mounted on a
base 18 which carries anodes (not shown) and is insulated from the base 18
by an insulating layer 16. Base 18 is supported by feet 19 and is coupled
to an electrical conductor 32 for coupling the anodes (not shown) to a
power source (also not shown). A removable cover 70 with crane handles 82
seals the upper lip 26 during operation. Those skilled in the art will
appreciate that this is the basic known configuration of an electrolytic
cell but for the placement and electrical coupling of the cathodes.
Referring now to FIGS. 1 and 2, cathodes 22 are electrically coupled to
cell wall 12 and covered with a membrane or diaphragm 24 as is known in
the art. Coupling of the cathodes 22 with a power source is made through
cell walls 12 as discussed above in the background of the invention. In
accord with the present invention, however, this coupling is made by a
conductor strap 40 which is mounted spaced apart from the steel cell wall
12 in one of several special ways to create a pocket between the strap and
the wall wherein a metal filler is placed.
Turning now to FIGS. 1, 2 and 3, it can be seen that in one embodiment of
the invention conductor strap 40 is mounted a spaced distance from the
cell wall 12 with end edges 44 of the strap and bottom edge 46a and top
edge 46b of the strap bent inward and welded, brazed or otherwise fastened
around its perimeter at 48 to the steel cell wall 12 so as to bound a
chamber or pocket 50 between the steel cell wall 12 and the strap 40.
Strap 40 is coupled to conductor 34 by means of a threaded bolt 35 or
other means known in the art. Conductor 34 is then coupled with a power
source (not shown) to supply cathodes 22. According to this embodiment of
the invention, pocket 50 is sealed by edges 44, 46a and 46b of strap 40 at
welds 48. Therefore, at least one hollow threaded filler plug 60 having a
cap 62 (or similar closable opening) is provided on strap 40 for access to
the interior of pocket 50. In accord with one embodiment of the invention,
pocket 50 is filled with metal filler 52 which enters pocket 50 in a
molten state through filler plug 60. Preferably, two or more plugs 60 are
provided, one located near the top of strap 40 as shown in FIG. 1 and
another located near the bottom of strap 40 as shown in FIG. 2 so that
pocket 50 can be partially or completely filled and drained when
necessary.
The selection of metal used as filler 52 is based on particulars such as
price and availability, but also on electrical and thermal conductivity,
coefficient of expansion, melting point, melting range, operating
temperature of the cell, ambient temperature of the cell environment,
desired electrical current density of the cell, concentration of brine
stock and desired quality of the end products, among other considerations.
Some suitable metals include, but are not limited to alloys containing
metals selected from the group bismuth, lead, tin, cadmium, indium,
silver, and copper.
As mentioned hereinabove, filler metal 52 may be an alloy which is liquid
at the operating temperature of the cell. By selecting such an alloy to
fill the interspace or pocket 50 between conductor strap 40 and cell wall
12, it can be assured that the entire surface area covered by the filler
metal is in continuous wetted contact and that the electrical contact
between the strap 40 and the cell wall 12 will be continuous and uniform.
Considering the density and surface tension of liquid filler metal, it can
also be assured that little or no electrolyte will be permitted to leak
through any small crack or defect in wall 12 and penetrate the interspace
or pocket 50. Thus, the conductor strap 40 and cell wall 12 will not trap
electrolyte in the interspace or pocket 50 and the contagion of
compounding corrosive attack which eventually destroys most electrolytic
cells of similar design will be prevented from its initial stage.
Moreover, because of the improved electrical conductivity of the cathode,
the entire electrolytic cell can be operated more efficiently over longer
periods of time.
Referring now to FIGS. 4 and 5, another embodiment of the invention can be
seen. Here the conductor strap 40 is mounted spaced apart from wall 12
with side edges 44 and bottom edge 46a bent inward and welded, brazed or
otherwise fastened at 48 to the steel cell wall 12 so as to bound a pocket
50 between the steel cell wall 12 and the strap 40. In this embodiment,
top edge 46b of strap 40 is kept spaced apart from wall 12 leaving an
opening at the top of pocket 50. In this embodiment, metal filler 52 can
be poured directly into the top of pocket 50 if molten or placed, dropped
or otherwise inserted into pocket 50 if metal filler 52 is solid. In the
case of molten filler, a drain plug such as plug 60 with cap 62 shown in
FIGS. 1-3 can be added to the strap 40.
There have been described and illustrated herein several embodiments of a
conductor strap for an electrolytic cell and methods of electrically
coupling the conductor strap to the cell wall. While the invention was
described primarily in terms of the apparatus invention, it will be
appreciated that the method invention is related directly thereto and
comprises steps such as forming a pocket defining conductive plate,
attaching the plate to the steel wall of the cell, filling the pocket
interspace between the plate and the wall with filler metal, etc. While
particular embodiments of the invention have been described, it is not
intended that the invention be limited thereto, as it is intended that the
invention be as broad in scope as the art will allow and that the
specification be read likewise. Thus, while particular metals such as
copper have been disclosed as constituting the strap, it will be
appreciated that other constituent metals could be utilized. Also, while
particular alloys for the metal filler have been discussed, it will be
recognized that other types of alloys could be used with similar results
obtained. Moreover, while particular configurations have been disclosed in
reference to the welding or otherwise attaching of the strap to the cell
wall, it will be appreciated that other configurations involving a
mechanical connection of the strap to the cell wall could be used as well.
In addition, while drain and filler plugs having threads and caps have
been disclosed, it will be appreciated that other similar devices for
filling and/or draining the pocket between the strap and the cell wall
could be used. Furthermore, while the electrolytic cell itself has been
disclosed as having a certain number of walls and electrodes, it will be
understood that different configurations of the electrolytic cell can be
used with the invention disclosed herein. Lastly, while an electrolytic
cell for the production of chlorine and caustic soda from saline
electrolyte has bee discussed, it will be understood that the invention
can be used with electrolytic cells for the production, concentration, or
purification of other chemicals as well and even for attaching conductors
to metal surfaces of devices other than electrolytic cells.
It will therefore be appreciated by those skilled in the art that yet other
modifications could be made to the provided invention without deviating
from its spirit and scope as so claimed.
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